Although there are various known types of fuel cells, one common type of fuel cell is a proton exchange membrane (PEM) fuel cell. The PEM fuel cell contains a membrane electrode assembly (MEA) provided between two flow field or bipolar plates. Gaskets are used between the bipolar plates and the MEA to provide seals thereat. Additionally, since an individual PEM fuel cell typically provides relatively low voltage or power, multiple PEM fuel cells are stacked to increase the overall electrical output of the resulting fuel cell assembly. Sealing is also required between the individual PEM fuel cells. Moreover, cooling plates are also typically provided to control temperature within the fuel cell. Such plates are also sealed to prevent leakage within the fuel cell assembly. After assembling the fuel cell stack is clamped to secure the assembly.
Preformed gaskets have been used to seal fuel cell components, see e.g., U.S. Pat. Nos. 5,176,966 and 5,284,714. The assignee of these patents, however, describes in U.S. Pat. No. 6,495,278 that such preformed patents tend to leak over time and that adhesive bonding of a membrane electrode assembly (MEA) to an adjacent pair of separator plates of a PEM fuel cell with epoxy resins, methacrylate resins, polyurethane polymers (PUR) or aliphatic polysulfides (ALIPS) reduces leakage.
Other document patents also describe the use of adhesives for bonding and sealing fuel cell components. For example, U.S. Patent Application Publication No. US 2001/00197790 describes the injection of a thermosetting silicone rubber into cavities of a PEM fuel cell to provide a formed-in-place gasket after sealing. Moreover, International Patent Publication No. WO 02/093672 A2 describes the use of a polysiloxane composition injected into fuel cell cavities to also adhesively bond the fuel cell components.
Furthermore, U.S. Patent Application Publication No. US 2001/0044042 describes the use of a thermosetting fluorine-containing material or a thermosetting silicone as a formed-in-place gasket material placed in grooves between separator plates of a fuel cell and in grooves between separator plates and membrane electrode assemblies of a fuel cell. The material used between the separator plates and the membrane electrode assemblies is described as being adhesive to bond these components. The material used between just the separator plates is described as being non-adhesive to permit replaceability of the components upon disassembly of the fuel cell assembly.
U.S. Patent Application Publication No. US 2002/0031698 describes the use of thermosetting silicone sealant to adhesively bond fuel cell components and the use of a thermosetting fluorine-containing sealant with low shear adhesive strength to non-adhesively bong the separator plates. The later sealant is described as being useful for providing stacked fuel cell assemblies with separability and rebuildability features. The sealants are described as being placed into grooves of opposing fuel cell elements. The opposing fuel cell elements are then placed together where the sealants are heated to cure the sealants and to seal and bond the elements.
The above-discussed preformed and formed-in-place gasket techniques, however, have not provided adequate sealing, have not been feasible or practical for mass production of multiple fuel cells, or have provided sealing at the expense of repairability or replaceability by adhesively bonding the various components of a fuel cell. Particularly, preformed gaskets do not generally compensate for fuel cell component tolerances or dimensional variabilities, and the above-discussed formed-in-place gaskets have not provided adequate sealability or repairability. Thus, there is a need for improved sealing compositions and methods for providing a fuel cell having both sealing and repairability.